As is well known, in a process of manufacturing glass sheet products as typified by glass substrates for a flat panel display and the like, a small-area glass sheet is cut out of a large-area glass sheet and an edge portion extending along each side of the glass sheet is trimmed off, to thereby dice the glass sheet. As a method therefor, a method of cleaving a glass sheet is taken as an example.
As one method of cleaving a glass sheet, there is known a cleaving method utilizing laser heating (hereinafter referred to as “laser cleaving method”) as illustrated in FIG. 7. In the method illustrated in FIG. 7, while moving a glass sheet G in an X direction along a preset cleaving line 4, the glass sheet G is irradiated with a laser beam 9 in a spot shape along the preset cleaving line 4 and a coolant 10 such as water is jetted following the laser beam 9.
Then, a thermal stress is generated due to a temperature difference between a heated portion 6 formed by heating the glass sheet G with the laser beam 9 and a cooled portion 7 formed by cooling apart of the heated portion 6 with the coolant 10. Through an action of the thermal stress, an initial crack 8 formed at an end portion of the glass sheet G is propagated along the preset cleaving line 4 and a cleaved portion 11 is continuously formed, to thereby carry out a full-body cleaving of the glass sheet G (see, for example, Patent Literature 1).